1. Field of the Invention
The present invention relates generally to a method and apparatus for transmitting information needed to allocate transmission resources to a User Equipment (UE) in a mobile communication system and, more particularly, to a method and apparatus for transmitting power headroom information of UEs in a mobile communication system.
2. Description of the Related Art
A Universal Mobile Telecommunication Service (UMTS) system is a 3rd generation asynchronous mobile communication system that uses Wideband Code Division Multiple Access (WCDMA) based on Global System for Mobile communication (GSM) and General Packet Radio Services (GPRS), which are European mobile communication systems.
The 3rd Generation Partnership Project (3GPP), now in charge of UMTS standardization, considers Long Term Evolution (LTE) to be the next-generation mobile communication system of the UMTS system. LTE, a technology for implementing high-speed packet-based communication at a transfer rate reaching approximately 100 Mbps, is expected to be commercialized in about 2010. To this end, several schemes have been discussed, including a scheme to reduce the number of nodes located in communication paths by simplifying the network structure, and a scheme to align wireless protocols and wireless channels, as closely as possible.
Referring to FIG. 1, Evolved Radio Access Networks (E-RANs) 110 and 112 are simplified to 2-node structures consisting of Evolved Node Bs (ENBs) 120, 122, 124, 126 and 128, and Enhanced Gateway GPRS Support Nodes (EGGSN) 130 and 132. A User Equipment (UE) 101 accesses an Internet Protocol (IP) network 114 by way of the E-RANs 110 and 112.
The ENBs 120, 122, 124, 126 and 128 correspond to the legacy Node Bs of the UMTS system, and are connected to the UE 101 by wireless channels. Compared with the legacy Node Bs, the ENBs 120, 122, 124, 126 and 128 perform more complex functions.
In the next-generation mobile communication system (hereinafter referred to as “LTE”), since all user traffic including real-time services such as Voice over IP (VoIP) is serviced through a shared channel, a device for performing scheduling by collecting status information of UEs is needed, and the ENBs 120, 122, 124, 126 and 128 are responsible for the scheduling. To implement the transfer rate of up to 100 Mbps, LTE uses Orthogonal Frequency Division Multiplexing (OFDM) as a wireless access technology in a bandwidth of up to 20 MHz. In addition, Adaptive Modulation & Coding (AMC) for determining a modulation scheme and a channel coding rate according to the channel status of the UE is applied.
An ENB (“base station”) receives reports on information received from the UEs (“terminals”) to perform an operation of allocating transmission resources to the terminals, i.e., to perform scheduling, and an example of such information may include Buffer Status Report (BSR) indicating information about the amount and type of data stored in the terminals, and information about power headroom of the terminals.
The BSR provides information indicating the amount of data stored in a terminal according to priority, and this information is generated and transmitted by the terminal to the base station if particular conditions are satisfied. The particular conditions may include, for example, a situation in which new data has occurred in a terminal that stores no data, and a situation in which a predetermined time has elapsed after transmission of BSR.
The power headroom information indicates the maximum available power that the terminal can use for uplink data transmission, given the current channel condition of the UE.
Although the size of the power headroom information is only a few bytes, 1 Resource Block (RB) which is the minimum transmission resource unit should be used to transmit the power headroom information, in view of characteristics of the OFDM communication system. Therefore, given that a total of 25 RBs exist in a system with a 5-MHz bandwidth, it is necessary to reduce the frequency of transmission of the power headroom information by generating and transmitting the power headroom information only when absolutely necessary.